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Keywords:

  • adaptation;
  • anxiety;
  • first-night effect;
  • personality trait;
  • polysomnogram;
  • sleep;
  • State Trait Anxiety Inventory

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. References

To clarify the effects of anxiety-related personality traits on sleep patterns, polysomnographic examinations (PSG) were performed over 4 consecutive nights on normal humans who tested within the low- or high-anxiety ranges. The subjects consisted of two groups of six male university students who scored either less than 45 points (low-anxiety group) or more than 55 points (high-anxiety group) on the Spielberger’s State Trait Anxiety Inventory. Compared to the levels of sleep change in the high-anxiety group, the low-anxiety group exhibited a greater change in REM sleep and stage 2 sleep. The REM sleep in the low-anxiety group was shorter on the first and second nights compared to the third and fourth nights, and the stage 2 sleep was longer on the first night than on the remaining three nights. Thus, the low-anxiety group showed a first-night effect followed by partial recovery on the second night, while the high-anxiety group exhibited no obvious first-night effect. These results suggest that there is a difference in sleep patterns, assessed by consecutive PSG, between those with low- and high-anxiety traits, and that anxiety-related personality traits attenuate the occurrence of the first-night effect, reflecting a lower adaptability to a novel environment.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. References

Various characteristic patterns associated with human sleep have been described, including morning or evening types (larks vs owls), good or poor sleep, and short or long sleep. Webb and Bonnet1 reported that larks tended to worry less than owls. Adam et al.2 indicated that poor sleepers were more anxious than good sleepers. Long sleepers have also been reported to show higher anxiety scores than short sleepers.3 Thus, these characteristics of human sleep may be closely related to the personality factors of individual subjects, particularly to the anxiety-related personality traits.

Anxious subjects show sleep disturbances such as prolonged sleep latency, shortened REM latency, and an increase in stage 1 sleep accompanied by decreases in stages 3 and 4 sleep.4 In addition, most persistent subjective insomniacs have high anxiety levels.5 Thus, anxiety seems to be one of the most important factors influencing sleep parameters and causing sleep disturbances in human subjects. To the best of our knowledge, however, no detailed study examining the effects of anxiety-related personality traits on electroencephalographic (EEG) sleep in normal humans has been made, although numerous sleep studies have been performed in order to examine insomniacs or neurotic patients with high-level anxiety disorders. In the present study, polysomnographic examinations (PSG) were performed on normal humans with low- or high-anxiety traits to investigate any difference in sleep patterns associated with anxiety-related personality traits.

METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. References

Subjects

Forty healthy male university students aged 20–31 years (mean 22.6 ± 0.4 years) were scored for their anxiety trait level using the Spielberger’s State Trait Anxiety Inventory (STAI).6 Twelve subjects were selected on the basis of their scores and assigned to two groups of six subjects: one group consisting of those individuals scoring less than 45 points and other of those individuals scoring more than 55 points on the STAI. The former group was designated the low-anxiety group (mean age, 22.2 ± 0.5 years) and the latter the high-anxiety group (mean age, 22.5 ± 0.8 years). Subjects who had a history of drug or alcohol abuse or of any medical, psychiatric or sleep problems were excluded. Resting EEG for all subjects in the present study were normal. Each subject gave informed consent prior to the study and was paid to participate.

State Trait Anxiety Inventory scores

The mean trait anxiety score of the low-anxiety group was 43.5 ± 0.7, while that of the high-anxiety group was 58.2 ± 1.6. The trait anxiety score of the low-anxiety group was significantly lower (P < 0.01) than that of the high-anxiety group (Mann–Whitney U-test).

The STAI is one of the most commonly used self-report measures of anxiety.6 Assessment of anxiety using this method is reliable for investigations in non-clinically anxiety-affected subjects.7 This test consists of separate self-report scales for measuring two distinct anxiety concepts: (i) state anxiety; and (ii) trait anxiety.

Since the purpose of the present study was to examine the relationship between anxiety-related personality traits and sleep in normal humans, the STAI trait scale was used to assess the anxiety level in the subjects enrolled in this study. Although the manner separating the subjects two groups who scored either less than 45 points or more than 55 points on the STAI is arbitrary, Endler et al.7 reported a much lower average STAI trait anxiety score (men: 41.5 ± 0.7; women: 42.3 ± 0.5) in 605 undergraduate students than was found in the high-anxiety group (58.0 ± 1.7) in the present study. In our previous study,8 however, 26 patients with anxiety neurosis showed a markedly higher average STAI trait anxiety score (62.5 ± 1.2) than the present high-anxiety group. Thus, the high-anxiety group in the present study may be considered to accurately represent normal humans with high-anxiety trait.

Experimental procedures

Polysomnographic examinations were performed over four consecutive nights on each subject in a private and sound-attenuated room in the laboratory. All subjects were drug-free and had refrained from alcohol and caffeine use throughout the study. Subjects were asked to refrain from napping and to maintain their usual activities during the day. At 21:00 h, while they rested in a quiet room, disc electrodes were attached to the subjects for PSG recording. The subjects were instructed to go to bed at 22:55 h. After lights-out, polygraphic recording began at 23:00 h and ended at 8:00 h the next morning.

Polygraphic recording

Polygrams were recorded according to the method described in the standardized sleep manual of Rechtschaffen and Kales.9 Electroencephlograms were recorded from Fz-A1 and C3-A2 using disc electrodes (International 10-20 Electrode system); the electro-oculograms (EOG) were recorded monopolarly from both canthi; and the electromyograms (EMG) were recorded bipolarly from the chin. Recording conditions for the EEG and EOG involved a time constant of 0.3, sensitivity of 10 μV/mm, and high-cut filter of 30 Hz, while those for EMG recording were 0.003, 3.5 μV/mm and 500 Hz. Polygrams were recorded directly on paper and simultaneously recorded with an analogue tape recorder (DRF-3915) for further computer analysis. In accordance with the Rechtschaffen and Kales sleep manual,9 all-night sleep stage scoring was evaluated for each 20 s period on the C3-A2 EEG by computer analysis using the interval histogram method.10 This system consists of a two-step analysis. The first step is the recognition of elementary patterns in the EEG, EOG, and EMG signals, and the second step is the determination of the sleep stage based on these parameters. In addition, visual analysis was performed using the blind technique to confirm the final evaluation of sleep stage. The sleep variables monitored in this study were total sleep time (TST) excluding periods of wakening, total wakening time (TWT) during a sleep episode, sleep efficiency (percentage of TST relative to the sleep episode), sleep latency (latency of initial stage 2 after lights-out), REM latency (latency of initial appearance of REM after sleep onset), total time in each sleep stage, and the percentage of each sleep stage relative to TST.

Statistical analysis

Statistical analysis of the sleep variables between the low- and high-anxiety groups was performed using Mann–Whitney U-test. Friedman’s non-parametric analysis of variance by rank was used for comparison of sleep variables between the 4 experimental nights within each group. When there was a trend or a statistically significant effect by night, differences between the first night and the subsequent nights were explored with Wilcoxon rank sum test.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. References

Sleep variables

The sleep variables of the low- and high-anxiety groups over the 4 consecutive nights are shown in Table 1. The low-anxiety group exhibited a significantly higher percentage of stage 2 sleep on the first night and tended to have a smaller amount and percentage of REM sleep on the first and second nights compared to the high-anxiety group. The low-anxiety group showed a longer sleep latency on the second, third, and fourth nights than the high-anxiety group, and a statistically significant difference was found on the third night. There were no significant differences between the groups in the TST, TWT, sleep efficiency, amounts of stage 1 and stages 3 and 4 over the 4 experimental nights.

Table 1.  . Sleep variables in low- and high-anxiety normal humans over four consecutive nights Thumbnail image of

In the low-anxiety group, a significant effect by night was found on the percentage of stage 2 sleep and a trend over 4 nights was observed on the percentage of REM sleep. The Wilcoxon rank sum test revealed that, in comparison with the first night, the percentage of stage 2 sleep decreased on the second, third, and fourth nights, and the percentage of stage REM sleep increased on the third and fourth nights in the low-anxiety group. In the high-anxiety group, a trend of night effect was shown on the amount of stage 2 sleep, with a significant decrease on the fourth night compared with the first night.

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. References

There were no significant differences between the high-anxiety and the low-anxiety groups in the TST, TWT, sleep efficiency, amounts of stage 1 and stages 3 and 4 over the 4 nights, although the amounts of stage 2 and REM sleep on the first and the second nights somewhat differed between the groups. No distinct differences between the two groups in the quality of sleep per se appear to exist. This is not unconvincing, since the subjects in the two groups, although having different anxiety-related personality traits, were normal students.

However, the two groups showed markedly different changes in the sleep variables across the 4 nights, respectively. Compared to the levels of sleep change in the high-anxiety group, the low-anxiety group exhibited a greater change in REM sleep and stage 2 sleep. The REM sleep in the low-anxiety group was shorter on the first and second nights compared to the third and fourth nights, and the stage 2 sleep was longer on the first night than on the remaining 3 nights. While similar changes also occurred in the high-anxiety group, the differences were more pronounced in the low-anxiety group, and the changes appeared sooner. It is well known that most persons show a first-night effect, mainly characterized by lower sleep efficiency, prolonged REM latency, a decrease in the amount of REM sleep, and an increase in the amount of stage 2 sleep, during their first night in a sleep laboratory.11[12]–13 Thus, in the present study, the low-anxiety group showed a first-night effect followed by recovery on the second or third night, whereas the high-anxiety group exhibited no obvious first-night effect.

It has been reported that psychiatric patients, including depressives and insomniacs, have a less marked first-night effect than normal controls.14[15][16]–17 However, there has been no report indicating how anxiety-related personality traits in normal humans affect the first-night effect, although Coble et al.18 demonstrated that, in a comfortable hotel-type environment, normal controls show no adaptation between first and second night. Thus, it is of interest that the first-night effect may be influenced by personality traits as well as by the sleep environment in normal humans, and that anxiety-related personality traits may attenuate the occurrence of the first-night effect. Nishijima19 claimed that extroverts with less anxiety adapt themselves earlier to a new environment than introverts with more anxiety. Thus, the low-anxiety group may have adapted to the laboratory earlier than the high-anxiety group, resulting in the apparent first-night effect with the recovery on the second night. In contrast, a lower ability to adapt to the laboratory may have resulted in the attenuated first-night effect in the high-anxiety group. A more global personality screening with a larger population is necessary to further clarify the relationship between the attenuated first-night effect and the personality or the nature of the attenuated first-night effect.

The low-anxiety group showed longer sleep latency on the second, third, and fourth nights than the high-anxiety group. The reason for this is difficult to explain; however, the fixed bedtime of each subject in the present study may be related to this problematic finding. The PSG recording time of 9 h may have been longer than desirable, particularly for the low-anxiety group, who are reported to be short sleepers.3 Thus, the TST might have been prolonged, and this might have reduced sleep pressure in the low-anxiety group, resulting in longer sleep latency on the second, third, and fourth nights than the high-anxiety group.

In conclusion, there may be a difference in sleep patterns, as assessed by PSG, between normal humans with low- and high-anxiety traits, and the normal subjects with higher anxiety-related personality traits may tend to show an attenuated first-night effect, reflecting a lower adaptability to a novel environment. Additionally, PSG data for several consecutive nights provide important information, including information regarding first-night effect and recovery from the effect. To confirm the present findings, however, we need to enlarge the sample size and employ various personality screening tests.

References

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. References
  • 1
    Webb WB & Bonnet MH. The sleep of morning and evening types. Biol. Psychology 1978; 7: 29 35.
  • 2
    Adam K, Tomeny M, Oswald I. Physiological and psychological differences between good and poor sleepers. J. Psychiatr. Res. 1986; 20: 301 316.
  • 3
    Webb WB. Are short and long sleepers different? Psychol. Rep. 1979; 44: 259 264.
  • 4
    Rosa RR, Bonnet MH, Kramer M. The relationship of sleep and anxiety in anxious subjects. Biol. Psychology 1983; 16: 119 126.
  • 5
    Morgan K, Healey DW, Healey PJ. Factors influencing persistent subjective insomnia in old age: A follow-up study of good and poor sleepers aged 65–74. Age Ageing 1989; 18: 123 126.
  • 6
    Spielberger CD, Gorsuch RL, Lushene RE. State-trait Anxiety Inventory. Consulting Psychologists Press, Palo Alto, 1970.
  • 7
    Endler NS, Parker JDA, Cox BJ, Bagby RM. Self-reports of depression and state-trait anxiety: Evidence for differential assessment. J. Pers. Soc. Psychol. 1992; 63: 832 838.
  • 8
    Kai S, Mashimoto S, Ikeda T, Kajimura N, Mizuki Y, Yamada M. Appearance of Fmtheta in neurotic patients. Jpn. J. Psychiatr. Neurology 1989; 43: 725 726.
  • 9
    Rechtschaffen A & Kales A. A Manual of Standardized Terminology, Techniques and Scoring System for Sleep Stages of Human Subjects. US Government Printing Office, Washington, DC, 1968.
  • 10
    Kuwahara H, Higashi H, Mizuki Y, Matsunari S, Tanaka M, Inanaga K. Automatic real-time analysis of human sleep stages by an interval histogram method. Electroencephalogr. Clin. Neurophysiol. 1988; 70: 220 229.
  • 11
    Rechtschaffen A & Verdone P. Amount of dreaming: Effect of incentive, adaptation to laboratory, and individual differences. Percept. Mot. Skills 1964; 19: 947 958.
  • 12
    Agnew HW, Webb WB, Williams RL. The first night effect: An EEG study of sleep. Psychophysiology 1966; 2: 263 266.
  • 13
    Schmidt HS & Kaelbling R. The differential laboratory adaptation of sleep parameters. Biol. Psychiatry 1971; 3: 33 45.
  • 14
    Mendels J & Hawkins DR. Sleep laboratory adaptation in normal subjects and depressed patients (first night effect). Electroencephalogr. Clin. Neurophysiol. 1967; 22: 556 558.
  • 15
    Kupfer DJ, Weiss BL, Detre TP, Foster FG. First night effect revisited: A clinical note. J. Nerv. Ment. Dis. 1974; 159: 205 209.
  • 16
    Hauri PJ & Olmstead EM. Reverse first night effect in insomnia. Sleep 1989; 12: 97 105.
  • 17
    Toussaint M, Luthringer R, Schaltenbrand N et al. First-night effect in normal subjects and psychiatric inpatients. Sleep 1995; 18: 463 469.
  • 18
    Coble P, Mcpartland RJ, Silva WJ, Kupfer DJ. Is there a first night effect? (a revisit) Biol. Psychiatry 1974; 9: 215 219.
  • 19
    Nishijima H. Relationship between the appearance of Fmtheta and habituation to the situation. 1982; 24: 701 707 (in Japanese).